Remote quantitative analysis of materials

ABSTRACT

The remote quantitative analysis of a material and the range of the material are determined from the Raman scattered radiation from the material, such as for example, a gas where the gas is subjected to intense pulses of laser radiation launched from a remote location. The scattered radiation is filtered to selectively attenuate reflected radiation from the source and transmit the Raman scattered radiation to a detector system which integrates the detected radiation over an interval spaced in time from a laser pulse whereby the spacing represents range to the gas and the integral represents the concentration of a particular species in the gas.

United States Patent 1 Leonard 1 1 Mar. 27, 1973 [541 REMOTEQUANTITATIVE ANALYSIS OF MATERIALS [75] Inventor: Donald A. Leonard,Stoneham,

Mass;

[73] Assignee: Avco Corporation, Cincinnati, Ohio [22] Filed: Jan. 22,1971 [2]] Appl. No.: 108,710

[52] US. Cl. ..356/75, 252/300, 350/312 [51] Int. Cl ..G01j 3/44 [58]Field of Search ..356/75; 350/312; 252/300 [56] References Cited UNITEDSTATES PATENTS 3,625,613 12/1971 Abell et al. ..356/75 3,528,740 9/1970Gerry et al ..356/75 X OTHER PUBLICATIONS Hirschfeld et al.Proceedings'of the Technical Program of the Electro-Optical SystemsDesign Conference", Sept. 1618, 1969, pages 418-427 Damen et al."Physical Review Letters", Vol. 14, No.

' 1, January 4, 1965 pages 9-11 Barrett et al. Journal of the OpticalSociety of American", Vol. 58, No. 3, March 1968 pages 31l-319 PrimaryExaminerWilliam L. Sikes Assistant Examiner-F. L. Evans Att0rney-CharlesM, Hogan and Melvin E. Frederick The remote quantitative analysis of amaterial and the range of the material are determined from the Ramanscattered radiation from the material, such as for example, a gas wherethe gas is subjected to intense pulses of laser radiation launched froma remote location. The scattered radiation is filtered to selectivelyattenuate reflected radiation from the source and transmit the Ramanscattered radiation to a detector system which integrates the detectedradiation over an interval spaced in time from a laser pulse whereby thespacing represents range to the gas and the integral represents theconcentration of a particular species in the gas.

ABSTRACT 3 Claims, 8 Drawing Figures L SPECTROMETER PHOTO- E MULTIPLIERf N02 90 5a so so a Z GATE PULSE AND AND 1 ND H GEN. I GATE F EG oR GATEFG'EG TORI IE I INTEG TORI l il l i L l J l l DELAY 7 //9] GE E" 6J3? lW GEN.II f A f I l I I t DELAY am q: 5 GENE 69 1 A Ff a i l 1 w 1 lRECORDER RECORDER RECORDER 502 Inez i N02 I 1 N2 PAIENIEUIIIRZYIEJYSSHEET 10F 5 l5 )6 TO "TARGET STEERING MIRRORS INTERFERENCE FILTER LIQUIDFILTER AND GATE MONOCHROMETER ILASER POWER CONTROL1- PULSED N2 LASER(MOPA) LASER TRIGGER -1 CIRCUIT PHOTO MULTIPLIER GATE PULSE GENERATORWAVELE NGTH ATTORNEYS PATENTEDmzmra 3,723,007

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DELAY i 53 GATE PULSE AND INTEGRATOR f GEN. I GATE I r DELAY GATE PULSEAND INTEGRATOR f GENII GATE 11 AND INTEGRATOR GATE PULSE 49 GEN. x

54 RECORDER DELAY 39 DONALD A. LEONARD INVENTOR.

BY myfm 0 140; ED QZZZ ATTORNEYS PATENTEUHARZYIQYS 723,007

SHEET 3 OF 5 T2 T LASER POWER CONTROL l4 I5 1 v T Y T l6 PULSED N2 LASERINTERFERANCE sTEERTNG Z To (MOPA) FILTER MIRRORS TARGET IfEYEP|ECEI'\,24 LASER a TRIGGER FROM CIRCUIT 22 23 TARGET LIQUID 54FILTER N 53 57 SP CTROMETER 59' 57 54 59 :1rsa QY\0\ MULTIPLIER 80 /T/ 460 T T j V GATE PULSE AND AND AND INTE GEN. I GATE TOR GATE 'NTEG TORGATE 6 1 T T U T T v\ T GATE PULSE GEN.H A f h A f E A f I A A l 9 I I E1 5 DELAY 7| 9 I L /|/99 T T T GATE PULSE J u L J 69 T ma T RECORDERRECORDER RECORDER 72f $02 102 N02 N2 DONALD A.LEONARD INVENTOR.

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ATTORN EYS PHOTOMULTIPLIER SIGNAL PATENTEUHARZYISR 3,723,007

SHEET u [1F 5 O 337| A LASER souncs 2 CO2 N02 CO2 0 NO co N20 2 N23WAVELENGTH A LASEI; 337IA I I l l J WAVELENGTH K DONALD A. LEONARDINVENTOR.

ATTORNEYS PATENTEUHARZYISTS SHEET 5 OF 5 WAVELENGTH DONALD A. LEONARDINVENTOR. BY M 772W WW f/ AM REMOTE QUANTITATIVE ANALYSIS OF MATERIALSThis invention relates to apparatus for remotely analyzing materials andmore particularly to apparatus for remotely analyzing gaseous materialsand determining the range thereto and the component gases thereof.

Remote sensing of gases in a gaseous effluent discharged into theatmosphere is described in US. Pat. No. 3,625,613 which is assigned tothe same assignee as the present invention. That application describes asystem which directs pulses of intense laser radiation from a remotetransmitter location to the gas effluent. Back-scattered radiation fromthe gas is detected and analyzed remotely to identify at least a few ofthe gas components of the effluent. The back-scattering is Ramanscattering and so exhibits Ramanshifted wavelengths which arecharacteristic of different gases. Selection of the scattered radiationby wavelength at a receiver location and measurement of the intensity ofthe selected radiation provides an identification of the particulargases and an indication of the relative concentration of each gas in theeffluent. In that system, the reflected radiation from the laser whichenters the receiver tends to mask the Ramanscattered radiation enteringthe receiver. This is compensated for in that system by purposelyselecting the reflected laser radiation at the receiver and subtractinga weighted signal representing the intensity thereof from themeasurements of intensity of the selected Raman-scattered radiation atthe receiver. This weighting is empirically determined and socalibration and determination of the weighting for each constituent gasis subject to inaccuracies and approximations. Furthermore, calibrationfor each constituent gas is accomplished with reliability only bytesting with each particular constituent in known concentration at aknown range from the transmitter and receiver.

It is an object of the present invention to provide such a system forremote monitoring wherein masking of Raman scattered radiation byreflected laser radiation at the receiver is avoided.

It is another object to provide in such a remote monitoring system meansat the receiver for blocking radiation of the laser radiation wavelengthwithout substantially attenuating the Raman scattered radiation at thereceiver.

It is another object to provide an improved calibration standard forsuch a system which preferably is intrinsic to the system.

It is another object that the calibration standard vary with range intrue representation of the effects of range on the intensity of Ramanscattered radiation at the receiver.

It is another object that the calibration standard vary with atmosphericconditions'in the path of the laser and the scattered radiation is atrue representation of the effect of such conditions on the intensity ofthe Raman scattered radiation at the receiver.

Remote monitoring of a gaseous effluent and par: ticularly a pollutingeffluent has among its purposes to identify the polluting gasconstituents and their concentrations in the effluent and also determinethe location of the effluent. Toward this end, the elevation, azimuthand range to the effluent relative to the known location of thetransmitter identifies the location of the pollution. Elevation andazimuth clearly define the direction of the pulsed laser beam. Rangedetermination is less apparent. Accordingly, it is another object of thepresent invention to provide such a remote monitoring system whichprovides within the basic system parameters for determining range to thegases which produce the Raman scattered radiation that enters thereceiver.

It is a further object to provide such a remote monitoring systemwherein there is produced at the receiver location sets of signalsarranged as to range and gas constituents.

It is another object to provide such sets of signals following eachlaser pulse.

In accordance with features of the present invention, intense pulses oflaser radiation may be directed to a gaseous target, such as, forexample, combustion products, water vapor in the atmosphere, effluentfrom industrial processes and the like, producing therefrombackscattered Raman radiation which is intercepted by .a receiverpreferably at the same location as the source of the laser pulses. Atthe receiver, the radiation is filtered to block, and thereby separate,reflected laser radiation from the Raman back-scattered radiation whichis separated by wavelength, detected and integrated over intervalsseparated in time from the laser pulse which produces thebackscattering. Each integral is representative of the concentration ofa given gas constituent and the time separation is representation of.the range to the effluent.

The present invention may also be used to quantitatively analyze liquidsand solids at locations remote from the laser source, such as, forexample, remote determination of temperature, salinity or impuritylevels in water or solid particulates suspended in a medium.

Other objects and features of the invention are apparent from thefollowing specific descriptions of embodiments representing the bestuses of the invention described in conjunction with the Figures inwhich:

FIG. 1 is a schematic and block diagram of an embodiment of a remote gasmonitoring system for determining the concentration of a specific gasconstituent at a specific range;

FIG. 2 is a plot of received radiation filter transmission vs.wavelength showing negligible transmission of reflected laser radiationwavelength;

FIG. 3 is a schematic and block diagram of another embodiment forrapidly determining the concentrations of a specific gas constituent ata plurality of ranges;

FIG. 4 is a schematic and block diagram of an embodiment for rapidlydetermining the concentrations of a plurality of gas constituents at aplurality of ranges;

FIG. 5 is a scale showing Raman scattered wavelengths for gas species ofinterest in air pollution when incident laser radiation is from a pulsednitrogen laser of wavelength 3,371A;

FIG. 6 is a plot of the receiver backscatter detector output versuswavelength for SOz-CO mixture subjected to the nitrogen laser radiationat 3,37IA and showing the measurement of $0 in the presence of CO FIG. 7is a plot of the receiver backscatter detector (photomultiplier) outputversus wavelength for airsubjected to the nitrogen laser radiation at3,371A and showing the Raman scattered radiation from O and N at theircharacteristic Raman shifted wavelength; and

FIG. 8 is a diagram showing the laser transmitter and receivermonitoring polluting effluent at a distant location.

When, for example, atmospheric gas species (constituents) are irradiatedby laser radiation, a Raman wavelength shift occurs with the resultantspectral lines being specific to the molecular species intercepting thelaser beam. Thus, the Raman shifted wavelength distinguishes each gasconstituent and the shifted wavelengths can be distinguished from themore intense laser beam reflection and Rayleigh scattering which doesnot shift wavelength. The Raman scattering technique as applied hereinto remote gas monitoring enables a range resolved measurement ofatmospheric constituents with respect to both species andconcentrations, all from a remote location.

Although other lasers may be used, the laser used in embodiments of thepresent invention is a 3,37lA ultraviolet pulsed nitrogen laser referredto as a master oscillator power amplifier (MOPA). In the MOPA a smallpulsed nitrogen laser is used as an oscillator to provide relatively lowpeak power pulses, about 10 KW peak power. The beam from the oscillatoris passed through a mode control spatial filter producing a beam of verylow divergence. This beam is amplified in a second larger laser unitwhich is pumped in synchronism with the oscillator to within onenanosecond.

The output of the MOPA is passed through an interference filter designedto pass a narrow line, the 3371A line and block spontaneous emissionlines from the nitrogen discharge. The MOPA laser is shown in FIG. 1 andindicated generally by the numeral 10. This laser includes theoscillator and amplifier 11, power source 12 and laser trigger circuit13. The trigger initiates laser pulses at a repetition rate of 100 ppseach of 10 nanosecond duration. The laser beam 16 is filtered by aninterference filter 14 which passes the narrow line 3,37 lA. Steeringmirrors 15 give fine direction control of the pulses l6 emanating fromthe laser and serve to steer the beam and position it within the fieldof view of telescope at the range ofinterest.

The telescope 20 provides the entrance to the receiver system denotedgenerally by the numeral 21. The telescope is a Newtonian type whichincludes a 10 inch mirror 22 having a 60 inch focal length. The focalsteering mirror 23 in the telescope directs entering radiation to theeyepiece 24 or to monochrometer 25. The eyepiece is used to sight thetelescope on the target. The monochrometer may be a Jarrel-Ash 5 1 metermonochrometer having a resolution of 17A per millimeter. It transmitsabout 20 percent in the ultraviolet and rejects stray light in the ratioabout 10".

A lens 26 at the exit slit of the monochrometer focuses the exit slit onthe field stop of photomultiplier 27. Between the monochrometer andphotomultiplier is a filter 28 which blocks the remainder of the 3,371Aradiation passed by the monochrometer 25 but passes the Raman shiftedradiation characteristic of the gas species under observation. Thefilter 28 may be radiation but is nearly completely transparent towavelengths of 3,50OA and longer. The purpose of the filter is to blockthe 3,371A radiation from the laser which is reflected from the targetgas (this may be a smoke plume) and which the monochrometer is not ableto reject fully.

FIG. 2 shows the filters characteristics, transmission vs. wavelength.As can be seen, transmission above 3,50OA is better than percent whilebelow 3,400A it is virtually zero. This particular water solutiondefined above is a simple cyclic Cyanine-like dye. Similar filters andtheir formulations are discussed in an article entitled TransmissionFilters for the Ultraviolet by M. Kasha, Journal of the Optical Societyof America, Vol. 38, No. ll. Filters in accordance with the presentinvention are preferred as their transmission characteristics are farsuperior to commercially available interference filters.

The effectiveness of the filter with characteristics shown in FIG. 2 ismore fully understood by considering the spectrum of Raman shiftedscattered radiation from the gas species likely present in a plume ofpolluting gas effluent. FIG. 5 shows the spectrum of Raman shiftedradiation for a number of gas species illuminated by 3,371A laserradiation. This includes 0 and N which of course are present in allatmospheric discharges. The relative intensities of backscattered 3,371Aradiation and Raman shifted scattering from O and N in the atmosphereare shown by the plot in FIG. 7. The plot is photomultiplier output vs.wavelength. The scattering from O and N at 3,55 7A and 3,658A,respectively, are weaker by more than three orders of magnitude than thebackscattered 3,371A. This illustrates the desirability of selectivelyblocking the 3,371A radiation at the receiver.

The resolution of the monochrometer determines the resolution of thevarious Raman scattered lines from different gas species and so itdetermines the resolution between gas species. Use of the water filterof the types described herein having characteristics such as shown inFIG. 2 permits the use of inexpensive monochrometers that need only beable to discriminate between the various Raman lines. A typical darkcurrent counting rate is 200 counts per second. However, when the outputof the photomultiplier is gated with nanosecond gate pulses at the rateof 100 pulses per second, the dark current count is less than 2 X 10 persecond. This illustrates the significant reduction in dark current countthat can be achieved by gating the output of the photomultiplier so thatthe output represents only the Raman scattered radiation from a givengas species at a given range from the laser. Ranging is intrinsic insuch a gate procedure, because, in effect, it looks at the receiveroutput at an interval which must relate to the laser pulse interval as arange interval. If the gate pulse interval is coincident with the laserpulse interval, then the range is zero. If it is delayed 100nanoseconds, after the laser pulse then the range is 50 feet and soforth. Thus, the effect of gating the output of the photomultiplier 27is two fold; it substantially reduces dark current pulses from thephotomultiplier and it limits the output to a specific range. For thesepurposes, the output of the photomultiplier which consists of electricalpulses representing incident photons of the Raman scattered radiation isgated and counted by the electronic circuit designated generally by thenu meral 30. This circuit responds to a trigger signal from the lasertrigger circuit 13. The trigger signals are delayed by delay 31 whichdetermines the range and feed to gate pulse generator 32 which shapesthe triggers into, for example, 100 nanosecond long gate pulses. Thesegate pulses are applied along with the output of the photomultiplier 27to AND circuit 33, the output of which triggers the counter 34. Thus,the counter produces a count number during the interval of a gate pulsewhich is indicative of the relative concentration of .a particular gasspecies at the target, the target being species at a multitude of rangesfrom the laser. Such an electronic system is shown in FIG. 3. Here, theoutput from the trigger circuit 13 is fed to each of channels denoted 40to 49 and is delayed between successive channels by, for example, equaldelays 39 which may.

be 50 nanoseconds. Thus, the trigger signal from the laser triggercircuit 13 is fed to the channels 40 to 49,

50 nanoseconds apart over a 500 nanosecond interval for 10 suchchannels. Each of the channels, such as for example, channel 40 includesa gatepulse generator 51 which responds to the trigger producing, forexample, a

3O nanosecond wide gating pulse. This gating pulse is applied to an ANDcircuit 52 in the channel and the output of the photomultiplier 27 isalso fed to the AND circuit 52. Thus, the output of AND circuit 52consists of pulses of equal amplitude and duration, each representing apulse output from the photomultiplier during the interval of the 30nanosecond gate pulse. These are counted or summed by an integratingcircuit 53 which may be an analog integrater or a counter. Theintegrater 53 produces an output signal level which represents theconcentration of the particular gas species identified by themonochrometer at the range designated by delay 31. Similarly, theoutputs from the channels 41 to 49 are signal levels representing theconcentrations of the same gas species at progressive ranges 25 feetapart. These outputs are fed to a recorder 54 for comparison withcalibration standards and analysis. One use of such a record is todetermine the smoke plume profile with respect to a specific gasspecies.

Clearly, the width of the monochrometer outputslit can be increased ordecreased to thereby correspondingly decrease or increase resolutionbetween Raman scattered radiation lines. If it is increased, then theoutput from the photomultiplier is greater and if it is decreased, thephotomultiplier output is decreased. Careful design and operation of thesystem permits resolution between Raman scattered lines less than IA. Ascan be seen from the spectrum of Raman shifted radiation from aselection of a typical gas species, shown in FIG. 5, the S0 Ramanshifted line is distinct from the CO and the NO lines and all of theseare distinct from the O and the N lines. A typical case is the detectionof 1 percent S0 in the presence of 99 percent CO which' represents atypical combustion fuel sulfur to carbon ratio. FIG. 6 shows Raman dataobtained with apparatus in accordance with the invention as shown forexample in FIG. 1. As clearly shown v in FIG. 6, S0 is clearlydetectable at the 1 percent concentration level. Hence, the system inFIG. 1 or the system in FIG. 3 is useful to identify a specific gasspecies or at least to distinguish the total concentration of a numberof gas species of particular interest in air pollution without includingthe O and N which are ever present. In addition, the electronics in FIG.3 enables the system to determine plume profiles with far less integration time than required with a single channel system having avariable input delay. With the system in FIG. 3, all the interestedranges are examined simultaneously and every laser pulse produces areceive signal indicative of the concentration of the selected speciesat all the interested ranges.

A series of monochrometers feeding a series of photomultipliers in thesystems shown in FIGS. 1 and 3 could be used to obtain a Raman scatteredreturn from a number of different gas species such as S0 N0 and CO;these being-the most serious air pollutants. All these species could beexamined as to concentration and range. A separate channel would berequired for each gas species responding to the output of the differentphotomultiplier as in FIG. 1 or a separate bank of channels respondingto the output of each photomultiplier would be employed as shown in FIG.3. It would be an advantage here to examine the gas species 0 or N whichare present in atmospheric gas effluents in known concentrations. Thechannel output for the known gas, 0 or N, would serve as a standard withwhich to compare the channel outputs for the other gas species. Thiscomparison would yield a measure of the relative concentrations of theunknown gas species to the known. A remote monitoring systemincorporating such a standard by which to compare the readings fromdesignated gas species in unknown concentrations is shown in FIG. 4.Here, the transmitter system including the pulsed laser 11, laser powercontrol 12, interference filter 14 and laser beam steering mirrors 15may be the same as described above with reference to the systems inFIGS. 1 and 3. In the receiver system 21 a Newtonian type telescope 22intercepts the scattered radiation which is directed by the steeringmirror therein to a spectrometer 53. A liquid filter 54 between thespectrometer and the telescope serves the same purpose as the liquidfilter 26 in the embodiments in FIGS. 1 and 3 and so may have the samecharacteristics as illustrated in FIG. 2. The spectrometer 53 separatesthe slits is detected by a separate photomultiplier. In a diffractiongrating spectrometer, the light from the telescope is rendered paralleland directed to a curved diffraction grating which separates the lightby wavelength by directing it to spaced slits which are identified withwavelength and so identify thegas species. The spectrometer 53illustrated in FIG. 4 represents either of these basic types and so itdirects radiation along three separate paths 54, S, and 56 to the fieldstops 57', 58 and 59' of photomultipliers 57, 58 and 59, respectively.Thus, the photomultipliers each detect a different wavelength of Ramanscattered radiation and so detect scattered radiation from a differentgas species. For example, the optical system may be designed so that thephotomultipliers 57 to 58 detect scattered radiation from the gasspecies S0 N0 and N respectively. The photomultiplier outputs areintegrated over pulse intervals which are related to the interval of alaser pulse. For each output a plurality of channels are provided, eachchannel producing a signal indicative of the concentration of theparticular gas species at a particular range. Thus, the output of eachphotomultiplier is treated by a plurality of range channels such asshown in FIG. 3 and so plume profiles of any particular gas or each ofthe gas species can be obtained following a single pulse from the laser.For this purpose, the output of photomultiplier 57 which represents theconcentration of S0 at the target range is fed to each of channels 60 to69. The delay 31 at the input to channel 60 and the delays 71 at theinputs to each. of the channels serve to delay the trigger signal fromthe laser trigger circuit 13 that is fed to the gate pulse generator ineach channel and so the gate pulses produced in the successive channels60 to 69 define the successive ranges just as in the system in FIG. 3.For example, if all the delays are 100 nanoseconds, then the ranges are50 foot increments.

The channels 60 to 69 may be identical to channels 40 to 49 shown inFIG. 3 and feed signals to the S0 indicator 72 which indicates the plumeprofile for S0 across a designated space.

Similarly, the output of photomultiplier 58 which represents theconcentration of N0 is fed to channels 80 to 89 which control the N0recorder 102. The output of photomultiplier 59 which represents theconcentration of N at a sweep of ranges is fed to channels 90 to 99which control the N recorder 1 12. The recorded N concentrations canserve as a standard because it is generally known in any atmosphericdischarge of combustion gases. Since the scattered Raman radiations fromthe three gas species are sensed simultaneously from substantially thesame optical paths (except for the photomultipliers) the signalsrecorded for the standard gas by the recorder 112 are useful as acalibration of all recorded signals.

The simultaneous measurement with apparatus in accordance with thepresent invention of CO S0 and NO can be used to unambiguously obtainthe ratio of SO to CO and NO to CO independent of the transmitter power,the optical transmission characteristics of the optical path and theplume or the amount of excess diluent air. Thus; by use of the presentinvention, SO /CO and NO/CO ratios may be easily measured and theseratios used to provide a standard for pollution enforcement, whichstandard would be as noted above, independent of dilution of effluent orpath transmission loss or transmitter power.

Each of the channels 80 to 89 and each of the channels 90 to 99 includesin the channel the gate pulse generator in the corresponding one ofchannels 60 to 69. Thus, the gate pulse generator 113 in channel 60which is the input to channel 60 is also the input to channel 80 and tochannel 90. Accordingly, channels 60, $0 and all respond to the samerange gate and their outputs are indicative of the concentration oftheir associated gas species at the same given range.

The system in FIG. 4 includes a number of significant features of theinvention and these features are related and somewhat interdependent.For example, the scattered radiation for each gas species is detectedand integrated only during the brief interval of a range gate pulsefollowing a laser pulse. This reduces the dark current count in thesystem and also insures detection of the Raman scattered radiation froma selected range. The advantages of the system shown in FIG. 4, asalready mentioned, are that separate gas species can be identified ateach of the succession of ranges from the laser and the concentration ofthese gas species at each range can be determined by comparing withequivalent signals received for N or other species which is in knownconcentration. Thus, the system in FIG. 4 enables the profile of apolluting gas effluent to be ob-.

tained simultaneously for a number of different gas species byilluminating the effluent with a single laser pulse. In practice,however, more significant output signals from the channels are producedwhen integration in each channel continues over a number of pulses fromthe laser. The number of pulses required to produce a reading willdepend upon, among other things, laser power, system sensitivity, bothoptical and electrical, and the concentrations of the gases which it isdesired to detect.

FIG. 8 is a diagram showing the remote laser transmitter and receiver ona pedestal 121 directing transmitted laser radiation 122 to a plume ofsmoke 123 emitted from a smoke stack 124. Scattered radiation 125 of allkinds returns from the plume to the receiver and is analyzed by thesystems such as shown in FIGS. 1, 3 or 4 to determine the constituents,concentrations and range to the plume.

The various embodiments of the present invention as shown and describedherein are intended to illustrate the best uses of the invention. Theseembodiments incorporate various features of the invention in differentcombinations to examine scattered radiation from a distant gaseoustarget. The apparatus described in these embodiments aides to determinethe gaseous species at the target, the relative concentrations ofdifferent gaseous species at the target and the distance to the target.Embodiments are also useful for determining the concentration profile ofa given gas species across a smoke plume and for determining thisprofile simultaneously for a number of different gas species so that thequality profile across the gas plume can be determined. The rangeinformation enables the location of an air pollution source to bedetermined. Variations of the embodiments of the invention describedherein are included within the scope of the invention as set forth inthe appended claims.

What is claimed is:

ll. In a detection system, the combination comprising:

a. a source of intense monochromatic radiation at 3,371 A which isdirected to a target, said radiation being in the ultraviolet range;

b. trigger circuit means for actuating said monochromatic radiationsource in a pulsed mode,

c. first means for detecting Raman scattered radiation of differentwavelengths which is scattered from said target due to the incidentintense monochromatic radiation, said first means comprising radiationseparation spectrometer means for receiving and separating Ramanscattered radiation of different wavelengths and photomultiplier meansfor receiving said separated Raman scattered radiation and producing aseparate electrical signal in response to each said separated Ramanscattered radiation;

. a plurality of sets of integrator means, each said set receiving andintegrating one of said electrical signal and providing a plurality ofseparate output signals for each said separate electrical signal;

. AND gate circuit means coupled to each integrator means for couplingits integrator means to one of said electrical signals;

f. means including gate pulse generator means actuated by said triggercircuit means and coupled to said AND circuit means for controlling theinterval of integration of said integrator means, the interval ofintegration of one each of said integrator means of each said set ofintegrator means being simultaneously controlled by a different gatepulse generator means, the controlled interval provided by each gatepulse generator means being differently spaced in time relative to saidpulses of said source;

g. indicator means for separately receiving and in- 30 dicating themagnitude of the said output signals of each of said sets of integratormeans; and a radiation filter in the path between the target and saidfirst means which transmits said Raman scattered radiation of differentwavelengths to said first means and blocks radiation of the samewavelength as the radiation from the source from reaching said firstmeans, said filter including a water solution of 2,7 dimethyl, 3,6diazacyclohepta, and 1,6 diene perchlorate having substantially completeisotropic volume bulk absorption at the wavelength of said radiation andonly small absorption of wavelengths of about 3,500 A and longer.

2. The combination as in claim 1 and additionally including delay meansactuated by said trigger circuit means for actuating said gate pulsegenerator means whereby each controlled interval of integration isdifferently spaced in time relative to a pulse of said source radiationby an interval indicative of the range from the source to the target.

3. The combination as in claim 1 and additionally including delay meansactuated by said trigger circuit means for actuating said gate pulsegenerator means whereby each controlled interval of integration isdifferently spaced in time relative to a pulse of said source radiationby an interval indicative of the range from the source of the target,and the outputs of said integrating means represent the relativeconcentrations of different gas species at specific ranges from thesource.

1. In a detection system, the combination comprising: a. a source ofintense monochromatic radiation at 3,371 A which is directed to atarget, said radiation being in the ultraviolet range; b. triggercircuit means for actuating said monochromatic radiation source in apulsed mode; c. first means for detecting Raman scattered radiation ofdifferent wavelengths which is scattered from said target due to theincident intense monochromatic radiation, said first means comprisingradiation separation spectrometer means for receiving and separatingRaman scattered radiation of different wavelengths and photomultipliermeans for receiving said separated Raman scattered radiation andproducing a separate electrical signal in response to each saidseparated Raman scattered radiation; d. a plurality of sets ofintegrator means, each said set receiving and integrating one of saidelectrical signal and providing a plurality of separate output signalsfor each said separate electrical signal; e. AND gate circuit meanscoupled to each integrator means for coupling its integrator means toone of said electrical signals; f. means including gate pulse generatormeans actuated by said trigger circuit means and coupled to said ANDcircuit means for controlling the interval of integration of saidintegrator means, the interval of integration of one each of saidintegrator means of each said set of integrator means beingsimultaneously controlled by a different gate pulse generator means, thecontrolled interval provided by each gate pulse generator means beingdifferently spaced in time relative to said pulses of said source; g.indicator means for separately receiving and indicating the magnitude ofthe said output signals of each of said sets of integrator means; and h.a radiation filter in the path between the target and said first meanswhich transmits said Raman scattered radiation of different wavelengthsto said first means and blocks radiation of the same wavelength as theradiation from the source from reaching said first means, said filterincluding a water solution of 2,7 - dimethyl, 3,6 - diazacyclohepta, and1,6 diene perchlorate having substantially complete isotropic volumebulk absorption at the wavelength of said radiation and only smallabsorption of wavelengths of about 3,500 A and longer.
 2. Thecombination as in claim 1 and additionally including delay meansactuated by said trigger circuit means for actuating said gate pulsegenerator means whereby each controlled interval of integration isdifferently spaced in time relative to a pulse of said source radiationby an interval indicative of the range from the source to the target. 3.The combination as in claim 1 anD additionally including delay meansactuated by said trigger circuit means for actuating said gate pulsegenerator means whereby each controlled interval of integration isdifferently spaced in time relative to a pulse of said source radiationby an interval indicative of the range from the source of the target,and the outputs of said integrating means represent the relativeconcentrations of different gas species at specific ranges from thesource.